1200 phrases and sayings and their origins! They also have fun categories, like fallacies (misattributed quotes, etc.)
Sayings and Phrases - meanings and origins
Of course, I have 3 books on the subject I haven’t read yet:
101 American English Proverbs Random House Dictionary Of America’s Popular Proverbs and Sayings Rawson’s Dictionary of Euphemisms and other Doubletalk